The present invention relates to an intake air system for a rotary engine and, more particularly, to an integral plenum chamber and tuned intake air conduit which receives cooling air from the engine and directs it to the carburetor for mixture and intake with fuel.
The rotary internal combustion engine has gained significant acceptance and is being used more widely in a variety of automotive applications. One of the major attractions of the rotary engine is its relative simplicity of construction as compared to more conventional reciprocating piston engines. In addition, advances in engineering technology have eliminated or substantially alleviated certain design and operational problems previously associated with rotary piston engines, such as rotor seal efficiency and life. As a result, additional applications for the rotary engine are marine use and, in particular, in outboard boat motors.
As with any other internal combustion engine where a flow of intake air is induced by operation of the engine, the intake of combustion air in a rotary engine may also be induced by engine rotation. A rotary engine may also often be air cooled or may include a combination of air and water cooling. If air cooling is utilized, cooling air flow is also induced by engine rotation. For the sake of convenience and simplicity of engine construction, a single flow of air is utilized both for engine cooling and for combustion. Thus, after a flow of air is directed through the engine rotor chamber of for cooling, it is directed into the carburetor or other combustion air inlet, mixed with the fuel and passed into the combustion region of the rotor chamber.
It is well known in the art of internal combustion engines, including rotary piston engines, that an induced flow of intake combustion air is not provided at a constant flow volume. Instead, the typical intake and exhaust strokes of an engine cycle (whether a two-stroke or four-stroke cycle) will result in a pulsed flow of air. The pulsed flow results in waves which travel back and forth through the intake air system such that the desirable maximum intake air volume is not always available for the intake stroke. Thus, a "tuning" or balancing of the intake air flow may be undertaken to provide a high pressure wave front pushing a maximum volume of air through the carburetor or combustion air inlet and into the combustion chamber at the most efficient point in the intake stroke.
Intake air tuning generally requires the use of an intake air conduit of substantial length but, depending upon the average engine speed at which performance is desired to be optimized, the length of the intake air conduit may vary substantially. The tuning length providing the best average performance for the specific application is, therefore, chosen with some resulting sacrifice in performance at other speeds. Unfortunately, the optimization of intake air flow in a rotary engine requires a tuned inlet air conduit of considerable length. Where a rotary engine is used in an outboard motor, the conservation of space and the need to keep overall engine size to a minimum are key considerations. Thus, the rather considerable length of an optimally tuned intake air conduit poses a significant space problem in an outboard motor application.
Another concern relating to available space in adapting a rotary engine for use in an outboard motor is the need to fit the engine into the typical enclosing envelope used for outboard motors. In particular, the rotary engine must be adapted to fit within the engine-enclosing cowl in a manner similar to a conventional reciprocating piston engine. The rotary engine is disposed with its rotor shaft extending vertically in the same manner as a conventional engine. However, with its combustion air inlet and exhaust manifold positioned rearwardly in the most convenient orientation, the width of the rotary engine block becomes a limiting factor when attempting to fit the engine into a conventional cowl. U.S. Pat. No. 4,911,122 shows an intake air inlet for a rotary engine which includes a plenum chamber and inlet conduit having a tuned length which are attached directly to the side of the engine block. However, when utilizing this construction in an outboard motor, the plenum chamber and outlet conduit occupy too much volume to fit within a conventional cowl envelope. Nevertheless, the plenum chamber volume and conduit length must be retained in order to provide optimum engine performance. Further, the general orientation of the rotary engine must also be maintained and, therefore, direct mounting of the plenum to the cooling air exit passage, as described in the above identified U.S. Patent, cannot be effectively utilized. In addition, that patent also discloses a large rearwardly disposed elbow connecting the outlet conduit to the carburetor inlet. This elbow occupies a large volume of space both to the side and the rear of the engine which also unacceptable when trying to fit the package into a conventional outboard motor engine cowl.